Electromagnetic actuator with permanent magnets



Aug. 5, 1969 A. TILLMAN 3,460,081

ELECTROMAGNETIC ACTUATOR WITH PERMANENT MAGNETS Filed May 51. 1967ATTORNEYS.

United States Patent 9 Claims ABSTRACT OF THE DISCLOSURE A bi-stableelectrically operated actuator suitable for use with valves, switches,or any other device that must be moved between positions at oppositeends of a stroke, and that must be held in position, selectively, ateither end of the stroke. The actuator has two permanent magnets, onefor holding it in each position, and it has electromagnetic windingsthat are temporarily energized to shift the movable element of theactuator from one position to the other. The movable element is aplunger which is made of material that is attracted by a magnet, but itis not itself a permanent magnet and it does not carry any of thewindings. The preferred embodiment operates without requiring anyreversal of the polarity of any of the magnetic poles of the actuator.

Brief description of the invention The invention is an improvedbi-stable solenoid of the type which has a plunger that is held,selectively, at either end of its stroke by permanent magnets; and thatrequires energization only during the time that the plunger is movingbetween different ends of its stroke.

The plunger is not itself a magnet, but it is made of material which isattracted by magnets. There is a different electromagnetic coil formoving the plunger in each direction. Although the permanent magnets arelocated at opposite ends of the plunger stroke, the stroke is longenough so that the distance from the disengaged magnet is sufiicient toprevent that magnet from adversely affecting the holding power of thepermanent mag net by which the plunger is held at any particular timeThe actuator is constructed so that the permanent magnets do not havedirect contact with the plunger and are not subject to direct shocksresulting from snap action of the plunger.

Other objects, features and advantages of the invention will appear orbe pointed out as the description proceeds.

Brief description of the drawing In the drawing, forming a part hereof,in which like reference characters indicate corresponding parts in allthe views:

FIGURE 1 is a sectional view through :an actuator made in accordancewith this invention; and

FIGURES 2 and 3 are sectional views, on a reduced scale, taken on thelines 2-2 and 3-3, respectively, of FIGURE 1.

Detailed description of the invention FIGURE 1 shows an actuatorincluding a housing which comprises a core 12 with a cylindrical opening14 extending throughout the full length of the core and preferablycoaxial with the core. There is a pole piece 16 in the left-hand end ofthe cylindrical opening 14; and a corresponding pole piece 18 in theright-hand end of the cylindrical opening. Each of these pole pieces 16and 18 is preferably a press fit in the core 12; and each "ice of thepole pieces may have a cylindrical bearing surface 20, coaxial with theopening 14.

The movable element of the actuator is a plunger 22 which slides freelyin the cylindrical opening 14 between confronting end faces 24 of thepole pieces 16 and 18. The plunger 22 contacts with the end face of thepole piece 16 at one end of the stroke of the plunger, and with the endface 24 of the pole piece 18 at the other end of the stroke. Thus thestroke of the actuator 10 is determined by the spacing of the polepieces 16 and 18 from one another.

The end faces of the plunger 22 are of complementary contour to the endfaces 24 of the pole pieces 16 and 18. In the construction illustrated,these faces are frustoconical, but it will be understood that they canbe flat or stepped, depending upon the desired shape of the power curveof the actuator.

There is an actuator shaft 28 connected with one end of the plunger 22.The drawing shows the shaft 28 with threads 30 that screw into theplunger 22. This is merely representative of a connection between theshaft and plunger, and these parts can be of one piece construction, ifdesired. The actuator shaft 28 slides axially in the pole piece 16.

At the other end of the plunger 22, the drawing shows another actuatorshaft 28', which is connected with the plunger 22 in the same way as theactuator shaft 28, and which slides axially in the pole piece 18. If theactuator is intended for a use requiring only one actuator shaft, theother actuator shaft 28 or 28' can be omitted. The plunger 22 is shownwith a uniform diameter between its end faces, but this is notessential, and the mid portion of the plunger 22 can be of reduceddiameter to decrease the friction surface, or the plunger can be made intwo portions connected together by a threaded element.

The core 12 has circumferentially extending cut-out portions in whichelectromagnetic windings 32 and 34 are located. Beyond these coils orwindings 32 and 34 there are annular permanent magnets 36 and 38,respectively. In the construction shown, the magnets 36 and 38 arebeyond the outer circumference of the coils 32 and 34 with the poles ofeach magnet axially spaced from one another, but these magnets can bebeyond the ends of the coils with their poles in radial relation to oneanother. The core 12, pole pieces 16 and 18, and the plunger 22 are madeof ferrous material, or other material which is a good conductor ofmagnetic flux.

The annular permanent magnets 36 and 38 are preferably of one-piececonstruction. There is preferably a ring 46, also of one-piece annularconstruction, for holding the magnets 36 and 38 in spaced relation toone another. An end ring 48 is preferably pressed over the end of thecore 12 to hold the magnets 36 and 38, and the ring 46 against axialdisplacement.

The rings 46 and 48 are preferably of ferrous material so as toconstitute a part of the magnetic circuit of the core 12. Theelectromagnetic windings 32 and the permanent magnet 36 are located sothat their poles are effectively at opposite sides of the gap betweenthe plunger 22 and the end face 24 of the pole piece 16 when the plungeris at the right-hand end of its stroke. Similarly, the electromagneticwindings 34 of the permanent magnet 38 effectively span the gap betweenthe other end of the plunger 22 and the end face 24 of the pole piece 18when the plunger 22 is at the left-hand end of its stroke.

In order to spread the magnetic flux and to concentrate it in theconfronting faces of the plunger and pole pieces 16 and 18, there aresections of non-magnetic material 52 inserted in the core 12 adjacent tothe gaps between these confronting faces. The sections 52 preferablyspan the gaps.

With the parts in the position shown in FIGURE 1,

the plunger 22 is held in contact with the end face 24 of the pole piece18. When winding 34 is not energized, the magnetic circuit is from thepermanent magnet 38, through ring 48 (if used), through core 12, polepieces 18, plunger 22, through ring 46 (if used) and the other end ofmagnet 38. Although there is a similar magnetic circuit at the other endof the plunger, the gap between the plunger and the pole piece 16 issufficient to weaken this other magnetic circuit so that it does notdetract substantially from the holding power of the magnetic flux at theright-hand end of the plunger 22.

The plunger 22 will remain in this position without expenditure of anyelectrical energy, until the winding 32 is energized to move the plungertoward the left. When this winding 32 is energized, it adds so muchadditional flux to the magnetic circuit of the magnet 36 that thecombined pull of the magnet 36 and the electromagnet formed by thewindings 32 is sufficient to overcome the holding power of the permanentmagnet 38, and the plunger 22 is moved to the left-hand end of itsstroke. The supply of energy to the windings 32 is then shut off, butthe plunger 22 remains in position at the right end of its stroke as aresult of the attraction of the permanent magnet 36.

Return movement of the plunger 22 to the right end of its stroke can beeffected at any time by energizing the winding 34 which adds to the pullof the magnet 38 sufliciently to overcome the holding power of thepermanent magnet 36.

In the construction illustrated, the plunger 22 has direct contact withthe end faces of the pole pieces 16 and 18; but non-magnetic gaskets orfacing can be used to produce a small magnetic gap between the ends ofthe plunger and the end faces of the pole pieces 16 and 18, if desired,while still leaving the end faces as the ultimate mechanical stops forlimiting the stroke of the plunger 22.

From the description of the operation, it will be apparent that theplunger 22 moves with snap action. This is highly desirable foroperating either valves or switches. The shock of the plunger instriking the stops, provided by the faces 22, at each end of the stroke,is not a direct shock on the permanent magnets 36 and 38. This protectsthe magnets and is an advantage over constructions which require thatthe plunger be a permanent magnet, or that the plunger strike againstpermanent magnets. The invention provides a bi-stable solenoid-operatedactuator which is firmly held in position at either end of its strokeand without requiring the energizing of the actuator coils at any timeexcept when the plunger is being moved.

The apparatus can also be operated by Supplying current to the magnetcoil at the end of the apparatus at which the plunger 22 is in contactwith the pole piece 16 or 18 and with the current in a direction to setup an opposing flux that nullifies the fiux of the permanent magnet sothat less force is required to move the plunger. In some designs thepermanent magnet at either end can be made strong enough to shift theplunger when the flux of the permanent magnet at the other end isnullified by its associated coil 32 or 34.

The preferred embodiment of the invention has been illustrated anddescribed, and the invention is defined in the claims.

What is claimed is:

1. In a bi-stable electromagnetic actuator including a core having anaxial opening therein, a plunger that slides back and forth in theopening as a bearing, stops in said opening at opposite ends of theplunger for limiting the reciprocating movement of the plunger to apredetermined stroke, the core, plunger and stops being made ofmagnetizable material, and an electromagnetic winding surrounding theopening near each end of the plunger, the improvement which comprises ashell around the outside of the core, plunger and stops, at least aportion of the shell comprising permanent magnets axially spaced fromone another and carrying the flux in the shell including that producedby the excitation of the winding, a different one of the permanentmagnets also surrounding the core at each end of the plunger.

2. The electromagnetic actuator described in claim 1 characterized bythe electromagnetic winding being divided between two separateelcctromagnets, one at each end of the plunger, the permanent magnetsalso including one at each end of the plunger, and magnetic insulatingmaterial between the magnets at one end of the Plunger and those at theother end thereof.

3. The electromagnetic actuator described in claim 1 characterized bythe core having confronting shoulders axially spaced from one another,the shell being held between the shoulders, one of the permanent magnetsbeing located with one of its pole faces in contact with one of theshoulders, the other of the permanent magnets being located with itsopposite pole face in contact with the other of said shoulders.

4. The electromagnetic actuator described in claim 2 characterized byeach of the permanent magnets being of annular cross section andsurrounding the outside of a different one of the electromagnets alongmost of the axial length of said permanent magnet and effectivelyspanning the locations at which there is a gap between the plunger andeach end stop when the plunger is in contact with the other stop.

5; The electromagnetic actuator described in claim 1 characterized bythe opening in the core having magnetic insulation in the side wallsthereof at the locations where there are gaps between the plunger andeach of the stops when the plunger is in contact with the stop at theother end of the stroke of the plunger.

6. The electromagnetic actuator described in claim 1 characterized bythe stops being elements inserted into the opening in the core atopposite ends of said opening, and one of the elements having an openingtherethrough of substantially smaller diameter than the plunger, and ashaft connected to the plunger and movable as a unit with the plunger,the shaft extending through the opening in the element that has theopening therein and being slidable in said element as a bearing.

7. The electromagnetic actuator described in claim 6 characterized byboth of the stops having similar openings therein coaxial With the axisof the opening in the core, and shafts extending from both ends of theplunger through the openings in the stop for connection with apparatusthat is to be operated by said actuator.

8. The electromagnetic actuator described in claim 1 characterized bythe confronting faces of the plunger and stops being complementary andat least a pair of one of the faces having a projecting portion thatfits into a recess in the confronting face to influence the force curveof the actuator.

9. The electromagnetic actuator described in claim 2 characterized bythe permanent magnets and parts of the core being rings that fit aroundthe other parts of the core and around the electromagnets and that stackon the core to form the shell of the actuator assembly.

References Cited UNITED STATES PATENTS 3,022,450 2/1962 Chase 335--229XR 3,040,217 6/1962 Conrad 335234 3,139,565 6/1964 Levine 335-2303,202,886 8/1965 Kramer 335234 3,381,181 4/1968 Weathers 335-230 XRGEORGE HARRIS, Primary Examiner US. Cl. X.R. 335-268 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Ltent No. 3,460,081 August 5,1965 Alfred Tillman It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected asshown below:

Column 4, line 51, "pair" shouid read part Signed and sealed this 21stday of April 1970.

1rd M. Fletcher, Jr.

WILLIAM E. SCHUYLER, JR sting Officer Commissioner of Patents

